Saturday, January 15, 2011

Brakes, Part III: Shoes and Drums

In a drum brake system the shoes are located inside of a drum which spins around an axle and to which the wheel is attached. Pressing the brake pedal forces the outer surface of the shoes--through hydraulic pressure--to contact the inner surface of the drum, slowing rotation of the drum and wheel, and stopping the car. Each time you brake a small amount of the brake shoe is worn away. A smaller amount of the drums (drums are cast iron) is also worn away; usually the wear on the drum is not exactly uniform, so over time the brake shoes need to be relined with new friction material, and the drums (usually) need to be turned, i.e. ground down until the surface is uniform and smooth (actually, not exactly smooth, but uniformly rough in order for the shoes to "grab" it better).

When I removed the drums on my car I got several surprises. First, the brake-shoe return system (the springs and clips that pull the brakes back into the "off" position when you release the brake pedal) was not installed correctly. Also, the shoes and drum were oil-soaked, a result of wheel cylinders that had leaked because of long-time inactivity. This is normal in cars put in storage for long time periods because small amounts of moisture inside the hydraulic (oil) system eventually corrode the metal. The rubber seals also degrade and both of these allow brake fluid to leak out of the system onto the shoes and drums. This does not usually occur if the car is used daily because even if there is a small amount of moisture in the system, braking causes it to move around so it doesn't have the chance to corrode a specific spot.

I knew before buying the car that I would have to replace at least some of the components of the hydraulic system ( I ended up replacing most of it), but after assessing the condition of the brake shoes and drums I realized I would also have to replace the shoes and turn (repair) the drums.

Before: Notice oil-soaked and corroded hardware.

After: Relined shoes, new wheel cylinders, cleaned hardware. The "hardware" is the springs at top and bottom and the two clips on the sides. I de-rested these Evapo-Rust, a very handy product to have on hand!

Hardware before Evapo-Rust

Hardware after Evapo-Rust

Freshly-turned drum. Isn't it pretty? I had Austin_Brake_&_Clutch turn the drums and reline the shoes. They have the proper equipment to turn these old-style front drums.

The threads on the axle were stripped. Here I am re-cutting the threads uing a die.

New tap and die set I bought from Harbor_Freight. The quality of the tools they stock is not as good as Craftsman,which I prefer, but they have a HUGE selection in stock, so you can usually find odd special tools there. I also bought my Evapo-Rust there.

After bleeding the brakes and adjusting the shoes the brake system is now restored and works as new, which was among the best, if not the best, in the industry for 1953. The Jul.-Aug. 1986, #94, issue of Special Interest Autos (now Classic_Car) road tested a 1953 Kaiser and said that "The large, 11-inch drum brakes pull the car down from 60 mph in about 225 feet (the same as a disc-braked modern car of this weight)." Not too bad for a 58-year-old car!

Here are the specifications, including brakes, for the 1953 Kaiser taken from the same issue of Special Interest Autos.